在酵母菌發酵中,氧氣的供給方式和速率,影響啤酒酵母(Saccharomyces cerevisiae) 代謝葡萄糖之模式。提高供氧速率,可提昇酵母菌的生長速率,但可能降低發酵產物(例如乙醇)之產率。發酵液之添加物,如消泡劑,可能影響溶氧質傳速率。酵母菌能在細胞內形成鉻-胺基酸之複合體,有助其糖之代謝。本研究探討啤酒酵母在不同供氧策略下,不同發酵液組成中,使用鉻離子的能力,期能使含鉻菌體成為附加價值較高之副產品。主要研究內容包括: 發酵液表面或底部噴流供氧,量測培養基在不同壓力下,達到飽和溶氧所需時間,培養基成份對溶氧的影響,以及壓力對於啤酒酵母菌生長與溶氧的影響。本研究計畫亦探討,以間歇方式供氧對於酵母菌生長的影響以及其對於酵母菌利用鉻之模式。發酵液中蛋白凍含量或種類,亦可能影響酵母菌對鉻之吸收或利用率。實驗顯示,以間歇方式供氧,與其他條件搭配,啤酒酵母使用鉻離子較佳之培養條件為: 接菌量1%、壓力2.5 psi、間歇供氧時間: 供氧4分鐘(壓力達設定值即停止)、排氣3秒、蛋白凍0.5%、糖濃度15%、發酵液中三價鉻濃度100 ppm,胞內鉻含量可達8 ppm。
In Saccharomyces cerevisiae fermentation,glucose metabolism is affected by the method and rate of oxygen supply. Increasing the rate of oxygen supplementation, although will increase cell growth rate, may decrease the product (e.g. ethanol) yield. Additives used in the broth, such as antifoam, could affect the oxygen dissolving rate. Baker yeast is capable of forming chromium-amino acid complex, to facilitate metabolizing sugar. This research investigated the yeast fermentation, under different conditions, the ability of the cells to utilize Cr3+ to increase the value of yeast cells as a by-product. The operation variables included method of aeration, pressure, timing of aeration, and Cr3+ concentration. Experimental data indicated that intermittently cycle of aeration to preset pressure then release pressure is preferred. Favorable operation conditions were 1% inoculum, aeration to 2.5 psi, sugar concentration of 15% (w/v), and 100 ppm Cr3+ in the broth. The aeration steps in one cycle were bubbling to 2.5 psi, hold pressure for 4 minutes then release pressure for 3 seconds. The cellular chromium could reach 8 ppm on dry weight basis.